1. Field of the Invention
Embodiments of the invention generally relate to tool control apparatus and methods. More specifically, the disclosed embodiments are directed to methods and apparatus for optically guiding a tool and/or the control of the work result of a tool that is moved relative to a workpiece in a straight or a curved path, for example. Non limiting example applications of the disclosed embodiments include the application of highly viscous masses such as adhesive beads or sealing beads, welding, soldering, marking, deburring, engraving.
2. Description of Related Art
The business and technology related to the application of highly viscous masses such as adhesive beads or sealing beads, welding, soldering, marking, deburring, engraving, e.g. (including controlling and guiding) is economically important.
The placement location and sizing of adhesive beads, sealing beads, pattern beads or corresponding structures (hereinafter, beads) formed by application of a viscous mass are typically controlled. In addition to correctly positioning the beads relative to the component, width can be controlled by means of two-dimensionally operating image analysis systems that use halftone pictures processing techniques. Applications such as, e.g., the window assembly in automotive engineering additionally require a height control and the control of observing the geometry of a special cross-section of a profile.
Known arrangements for width and position control may use a sensor comprising a camera and an illumination setup, basically aligned to each other in a manner where the illumination incidence angle equals angle of reflection). For the height control or profile cross-section control, light section methods (triangulation by means of structured light) are currently typically used, e.g., one or more laser lines and a camera for capturing the reflected light. For “online” control, i.e., for control during the bead application, the sensor may be typically mounted in the vicinity of the application nozzle and is in general fixedly connected to it.
During bead application, the application nozzle moves relative to the workpiece on which the bead is applied. It is thus basically irrelevant whether the nozzle moves while the workpiece is fixed or vice versa.
With regard to online control, the camera should be directed at the area behind the application nozzle. When the application paths are curved, the sensor has to be turned around the application nozzle in order to constantly record the area behind the application nozzle. Such turning is also desirable when shaped beads are applied. If the nozzle is moved by a robot, the robot may effect the turning. If the nozzle is stationary and a part is moved by the robot, the robot may also effect the turning. However, in the case of large parts as they are common in car manufacturing, a lot of space may be required. If the required space is to be reduced, extra turning means will be required. Alternatively, when used together with extra turning means, simple and cost-effective x-y systems may replace robots.
However, extra turning means should be avoided for the sake of expenditure. In this context, e.g., DE 20307305 U1 discloses that monitoring means with one or more cameras can be fixed at the tool such that the visual range of the camera(s) is always directed to the working area and/or a fixed monitoring area in case of movement of the tool and/or an object to be processed. With several cameras on a concentrically arranged circle provided with a cut-out for the tool, a basically circular monitoring area can be realised which is created by the visual ranges of the several cameras. Thus the monitoring area is basically independent of the alignment of the tool. According to the referenced disclosure, monitoring around the tool requires at least two cameras with overlapping working/monitoring areas. An arrangement with only one camera suitable for complete control is not indicated.
Similar arrangements requiring several cameras are disclosed in WO 2005/065844, WO 2005/063406, WO 2005/063407. In all cases, at least two cameras, and often, preferably, three are required to create a monitoring area around the workpiece A disadvantage of these arrangements is that several cameras are generally necessary whose pictures even have to be analysed at the same time. Furthermore, a greater amount of space is required transverse to the movement direction. This is particularly disadvantageous when the bead is to be applied under cramped space conditions (e.g., along steep profiles). Other disadvantages include disturbances in illumination due to shadowing. Moreover, these arrangements may not be suitable for a height controller only with several or more cameras.
When the tool is guided by an optical sensor, e.g., when tracking an edge, a groove, a weld bead, or when selectively setting the movement by means of “landmarks” such as holes or edges, the same problems and disadvantages may be present: according to the prior art so far. Thus, it would be beneficial and advantageous to provide a system requiring only a single camera in place of the several guiding cameras which are necessary to avoid a turning movement with respect to a curved path, with great differences in direction.